Method of securing decorative matter to a surface of a polyethylene body



1, 1953 M. F. KRITCHEVER 2,648,097

METHOD OF SECURING DECORATIVE MATTER TO A SURFACE OF A POLYETHYLENE BODYFiled April 4, 1952 l7 COOLED RO L LER IDLER LLER PRINTABLE SURFACEPRINTING UNIT I NVEN TOR.

ATTORNEYS.

Patented Aug. 11, 1953 UNITED STATES PATENT OFFICE METHOD OF SECURINGDECORATIVE MAT- TEE TO A SURFACE OF A POLYETHYLENE BODY Mathew F.Kritchever, Wilmette, Ill., assignor to Traver Corporation, Chicago,111., a corporation of Illinois Application April 4, 1952, Serial No.280,583

2 Claims. (01. 18-475) This invention relates to the manufacture ofprinted for a relatively short time without raising a printable surfaceon resinous films and plastic the mass of the plastic to a temperatureenabling materials which have heretofore been considered distortion. Ifthe plastic material is in the form unreceptive to coating compositionssuch as to r of a film of thin sheetstock, itis expedientto, obviatesatisfactory printing or coating thereof. direct the flame onto thesurfaces of'the plastic The present application is acontinuation-inwhile the opposite wall is being cooled. If the part ofmy co-pending application, Serial No. flame directed onto the plasticsurfaces is in ex- 150,414, for Treating Polyethylene Plastics For cessof 1300 F., preferably withinthe range of Printing, filed March 18,1950. 1300-1600 F., almost instantaneous conversion In most respects,anchorage of the printing m to a highly ink-receptive surface issecured. If or coating compositions on various types of surlowertemperatures are employed, it may be faces depends upon some type ofphysical or necessary to prolong the flame treatment or to chemical bondexisting between the coating or provide successive treatments, keepingin mind printing compositions. and the surfaces upon that the plasticshould not be heated through which they are to be applied. When printingon to a temperature permitting plastic flow. Inany,

paper or other porous surfaces, anchorage of the event it is seldom thatmore than a second or printing ink or coating composition is achieved afraction of asecond is required. by partial impregnation andinfiltration of the At present, beneficial results have been onlycomposition into the pores of the fibrous strucachieved by directcontact of aflame with the ture which enables the development of a firmplastic surface. For purposes of illustration but gripping relation withthe surface in a type of not of limitation, apparatus for carrying outthis physical interlocking. When printing or coating invention by meansof a gas flame will herein: onto smoother surfaces, such as plastic,glass or after he described in connection with the acthe like, relianceis usually had upon a physicocompanying drawing in whichchemical bond,such as softening of the material Figure 1 is a perspective plan view ofapparatus on the plastic surfaces to be printed, as by means forcarrying out the invention on plastic film of a mutual solvent, to makepossible a type of stock; Figure 2 is a sectional elevational viewintegration of one material with the other. of the arrangement ofelements shown in Figure With a material such as polyethylene, the pos-1; and Figure 3 is .a sectional elevational view sibilities foranchorage in the usual manner are 3\ which schematically shows thetechnique for cars substantially absent. This is especially true withrying out the invention on an already formed polyethylene plastics, themolecules of which have plastic container.

been orientated by stretching while in plastic As shown in Figures 1 andf the drawing, a condition and then setting as in the manufacture gasflame H1 is directed onto a surface of a film of film or sheet stock.The difficulties with l! of polyethylene While the opposite surface isprinting on polyethylene surfaces apparently being ,cooledas the filmpasses over a water-. arise from the smoothness of the surfaces, whichcooled roller I2. The flame I2 is generated by militates against purelyphysical anchorage, and gas which flows from a plurality of spacedorifices the inertness of the resinous polymers which IS in a manifold I4. In the alternative, gas may militates against development of a bondthrough in be supplied from an elongated slot across the the techniqueof eating into the surfaces to be orifice to provide an endless flame.In the event printed by solvents or the like, usually embodied that thetemperature of the flame directed onto in the printing or coatingcomposition. I the outer wall of theplastic. film is below that In viewof the increasing use of polyethylene capable of effecting.- the desiredconversion .to in the form of film, sheet stock, or containers for aprintable surface" by instantaneous contact, packaging, it becomesimportant to provide a systhe speed of the roller or the travel of theweb term which permits printing thereon, on a mass maybe slowed, butitshould not be slowed to production basis, characteristic of modernpacka rate which permits the flame to heat the agingtechnique. It is anobject of this invenplastic through to a temperature permitting distionto overcome the difliculties of printing or tortion. In the event thatthe instantaneous coating onto polyethylene. contact of the flame isincapable of giving the In accordance with this invention, a surfacedesired result, it is better to provide a number highly receptive to thecommon ink and coatof such manifolds to direct separate flames onto ingcompositions is developed on polyethylene by the surface of thefilm asit travels over the cooldirecting a gas flame onto the surfaces. to being roller I 2," or to provide a plurality of such individual units forsuccessive treatments of the type described. After the surface of theplastic film has been flame treated in the manner described, the surfaceof the plastic is thereafter highly receptive to ink and coatingcompositions ordinarily used in the printing and packaging trade. As aresult the film can be processed immediately or any time thereafter inthe usual manner in the printing trade. Without causing distortion inthe body of the plastic or releasing the internal stresses of theplastic body, thesurface is thus rendered permanently receptive oradherent to ink, coating compositions, or other decorative matter.

The flame treated plastic film I 5 may be passed over one or more idlerrollers l6 and then packaged for subsequent printing and use in themanner intended, or else it may be advanced directly to a printing unitI! to ink the prepared printable surface.

In the present systems for molding or blowing plastic containers, suchflame treatment prior to the formation of the container is practicallyimpossible, and, after formation, treatment in a manner described forfilm and sheet stock is equally unavailable. It has been found, however,that concepts of this invention may be practiced with relatively thicksheet stock and plastic bodies, such as exist in molded and blowncontainers, by passage of a gas flame quickly over the surface to beprinted without heating the mass of the plastic to a temperaturepermitting plastic flow.

As illustrated in Figure 3, a blown polyethylene bottle 20, with orwithout a coolant therein, may be dropped or passed through a ringmanifold 2| for directing a flame 22 onto the surface of the plasticbottle as it passes therethrough. If a single passage is not sufficientto provide the desired printable surface on the bottle, the bottle maybe passed through the flame more than one time or a series of suchmanifold flame-generating units may be provided in spaced-apart relationto effect such treatments in successive fashion. In the event that theplastic material is in the form of sheet stock, it may be passed overthe flame or a flame may be passed over it without relying on contact ofthe opposite surface with some coolant, so long as the contact of theflame is insufficient to heat the plastic to flowable condition.

By this simple technique, I have succeeded in providing printablesurfaces on plastic materials which have heretofore been unreceptive toink or resinous coating compositions. The

theory upon which the reaction may be based is not understood for thepresent. It might be that the flame treatment casues a type ofrearrangement of the molecules which exist on the surface of the plasticwhereby a new type of anchoring relation is permitted with the appliedink or coating composition. It might also be that some type ofmodification occurs in the molecules that exist on the resinous surfacewhereby a flame treated surface only becomes printable and receptive tocoating composition. Whatever the reason, the results achieved indicatethat a new relationship exists which makes these flame treated resinousmaterials and plastics more suitable in the packaging field because ofthe greater ease and permanence of printing with ordinary inks. As asresult, it is unnecessary to provide an auxiliary wrapping to carry thenecessary printed information, as is the practice for the present.

The heating of the surface or the impingement of the flame thereonapparently changes the structure of the surface polyethylene moleculesto render them adherent to decorative matter, and the application of theheat or flame is discontinued before distortion of the interior of thepolythylene body occurs and before the treated surface tends to flow orlose its contour. Upon cooling, the surface hardens and the hardenedsurface, having its original contour unmodified, is thus maintainedpermanently receptive and. adherent to decorative matter.

Tests made upon the treated polyethylene body indicate that the surfacepolyethylene molecules are modified Very substantially by the creationof double bonds. A relatively high degree of unsaturation of the surfacepolyethylene molecules is produced by the heat treatment, causing thesurface to become new highly receptive to inks, pigments, adhesives,coating compositions, and other decorative matter. The surface is cooledto harden it in this condition, so that the unsaturated surfacemolecules continue permanently to be receptive to such added matter. Thetests further show that should the heating be continued to the pointthat plastic flow of the treated surface is brought about and thecontour of the surface modified, this receptive or adherent quality islost. Flame treatment is, therefore, discontinued to avoid plastic flow,thereby maintaining the original contour of the article being treated.

Tests have been made to determine he effect of the flame treatment of apolyethylene film in comparison with a film which was not subjected tosuch treatment. In the tests, film A was an untreated control. samplehaving a thickness of 1.3 mil. Film B was a thermally-treated filmhaving a thickness of 2.25 mil. These films were run through a Beckmanrecording infrared spectrophotometer, with the results indicated below.

In the infrared study of chemical changes in polyethylene films, it isimportant to compare carefully the recorded trace of the test samplewith that of the control. The most significant change noted in studyingfilm B as compared to film A was the increase in the amount of R2C=CH2groups. These groups are produced by the degradation of the long chainsprobably at points along the chain. where the side branches areattached. Unsaturation is also tested quantitatively by measuring theweight of bromine vapor absorbed by the film in the dark. The bromine ispumped out of the film as much possible after exposure (the length ofexposure may be as long as several days), but for a surface treatment, afew minutes or hours is all that is required. Control experiments arecarried out at the same time, using untreated sam,

Polyethylene does not oxidize at an appreciable rate when in the solidstate unless activated by gamma rays, electron bombardment, etc. As aliquid, it will combine readily with if oxygen is present only in minutepercentage in the gas to which the liquid polyethylene is exposed.

The tests upon film B not only gave evidence of the production of theC=O group at 5.9 ,1, but also some evidence of oxidation because ofgeneral increase of absorption between 8 and 10 There is a slightintensification of the RCH- CHZ absorption band at 11.3 indicatingproduction of double bonds.

The treatment of the film or other polyethylene body with flame Verysubstantially increases the number of unsaturated linkages while alsooxidizing the surface of the film. The heating is carried on to thepoint that a softening of the treated surface occurs, but the heating isdiscontinued before plastic flow is brought about causing a change ofcontour of the surface. Upon cooling, the hardened surface remainspermanently receptive and strongly adherent to inks, pigments,adhesives, coating compositions, and other forms of decorative matter.Treating with flame is highly effective in bringing about the softeningwithout plastic flow to produce the high receptivity required in thatthe flame supplies high heat for a brief moment and the period ofphysical contact is terminated before plastic flow of the surface occursor distortion within the interior of the polyethylene body occurs. Ifind it advantageous to employ a flame having a temperature of from 1300or 1600 F. up to 3600 or 3800" F. I prefer to employ a flame temperaturein the neighborhood of 3600 F. because the period of exposure of theplastic surface to the flame can thus be considerably shortened.

The flame-treated product, whether it be a flame-treated polyethylenefilm or a relatively thick polyethylene body, is characterized by a verysubstantial increase in the number of double bonds. The unsaturatedsurface molecules produced by the flame treatment cause the surface,even when hardened, to maintain a high aflinity for inks, pigments, andother forms of decorative matter.

It will be understood that numerous changes 6 may be made in the detailsof handling, cooling, or applying the technique without departing fromthe spirit of the invention, especially as defined in the followingclaims.

I claim:

1. The method of securing decorative matter to a surface of apolyethylene body, which comprises passing said surface of saidpolyethylene body through a flame to immerse said surface within saidflame to soften said surface without materially heating the rest of saidbody, then permitting said surface to harden and set to produce asurface permanently adherent to decorative matter.

2. The method of securing decorative matter to a surface of apolyethylene body, which comprises maintaining a flame having atemperature of from 1600 to 3800" F., passing said surface of said bodythrough said flame to immerse said surface in said flame to an extentsuflicient to soften said surface, withdrawing the surface of said bodyfrom said flame before materially heating the rest of said body, thenpermitting said surface and body to harden and become set to produce asurface permanently adherent to decorative matter, and thereafter at anytime applying decorative matter to said permanently-receptive surface.

MATHEW F. KRITCHEVER.

'No references cited.

